TitleClaw morphology, prey size selection and foraging efficiency in generalist and specialist shell-breaking crabs
Publication TypeJournal Article
Year of Publication1998
AuthorsYamada, SB, Boulding, EG
JournalJournal of Experimental Marine Biology and Ecology
Type of ArticleJournal Article

Claw morphology, and claw-closing forces of four species of intertidal crabs from San Juan Island, Washington were compared and related these findings were related to prey size selection, shell breaking times and total handling times on their snail prey, Littorina sitkana Philippi. Two functional groups of crabs emerged: generalists and specialists on hard-shelled prey. The generalist, Hemigrapsus nudus (Dana), has an omnivorous diet and possesses weak claws with small, fine denticles and mechanical advantage (MA) of the claw's lever system 0.3. The claws of the generalist, H. nudus, exhibited weaker claw closing forces (5 N) than those of similar sized specialists (>12 N). When crabs of similar weight were offered four size categories of Littorina sitkana, the generalist, Hemigrapsus nudus, exhibited a consistent preference for the smallest size categories, while the three specialists attacked all size classes offered. Hemigrapsus nudus took significantly longer (134 s) than the specialists (30-52 s) to break open a 4 mm L. sitkana. This difference in shell-breaking time between the generalist and the specialists increased with increasing prey size. The rate of successful attacks on increasingly larger L. sitkana decreased with prey size in the generalist (70% on 4 mm, 37% on 6 mm, and 0% on 8 mm snails), but remained high in the specialists (70-100%). Strength limitation of the claws is the best hypothesis to explain the avoidance of large snails by the generalist, H. nudus. (C) 1998 Elsevier Science B.V.

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